1. Field of the Invention
The present invention relates to a temperature compensation device for an automatic gain control loop used in a wireless communication unit.
2. Description of the Related Art
In general, a mobile communication terminal measures the strength of a received signal, and reduces or increases the gain of an amplifier if the measured strength is found to increase or decrease, respectively, to maintain received power at a desired level. The terminal also determines the strength of a signal to be transmitted depending on the received signal strength.
FIG. 1 is a block diagram showing an example of a conventional receiver of a mobile communication terminal. As shown in this drawing, a radio frequency (RF) signal received through an antenna is converted into a digital signal through a low-noise amplifier (LNA) 101, band pass filter (BPF) 102, frequency mixer 103 and analog/digital converter (ADC) 104. The digital signal from the ADC 104 is applied to an energy detector 106, which measures the strength of the received signal from the applied digital signal. The energy detector 106 then adjusts the gain of a digital variable gain amplifier (DVGA) 105 through a gain determiner 107 such that the received signal strength becomes a desired signal level. The gain determiner 107 also adjusts the gains of the LNA 101 and frequency mixer 103 according to the received signal strength.
FIG. 2 is a block diagram showing another example of the conventional receiver of the mobile communication terminal. As shown in this drawing, an RF signal received through an antenna is converted into a digital signal through an LNA 201, BPF 202, frequency mixer 203 and ADC 205. The digital signal from the ADC 205 is applied to an energy detector 206. The energy detector 206 measures the strength of the received signal from the digital signal applied from the ADC 205. The energy detector 206 then adjusts the gain of the automatic gain controller (AGC) 204 through a gain determiner 208 such that the received signal strength achieves a desired signal level. Note that the AGC 204 must be controlled by an analog signal since it is an analog device. In this connection, a gain adjustment signal from the gain determiner 208 is converted into an analog signal through a pulse density modulation (PDM) generator or a digital/analog converter (ADC) 207 and is then applied to the AGC 204 to adjust the gain thereof. The gain determiner 208 also adjusts the gains of the LNA 201 and frequency mixer 203 according to the received signal strength.
As mentioned above, it is necessary to accurately measure the strength of a received signal in conventional mobile communication terminals. However, the amount of gain or loss of each component in the receiver of the mobile communication terminal varies with temperature, resulting in errors in the measured signal strength.
Recently, direct conversion type chips, which can directly convert a received signal into a baseband signal without using an intermediate frequency, are being used in receivers of mobile communication terminals. In this case, in order to secure a dynamic range of the receiver, a number of gain adjustment components, such as a low-noise amplifier, frequency mixer, baseband variable gain amplifier, etc., are used and a number of gain adjustments are made with variations in the received signal strength. As a result, because the various components will provide differing gain as the temperature varies, errors may occur in the measurement of the received signal strength, resulting in generation of an inappropriate gain adjustment signal and, in turn, deterioration of transmitter and receiver characteristics.